Patent GB-1225061-A (GB)
Title: Manufacturing semiconductor devices
IPC: H01L21/00
Filed: 1968-02-22
Abstract: 1,225,061. 061. Electrolytically etching semiconductors. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Feb. 22, 1968 [Feb. 25, 1967], No.8639/68. Heading C7B. [Also in Division H1] In a process for the removal by electrolytic etching of low resistivity semi-conductor from a relatively high resistivity zone which is to be retained, the etching contact is provided at a point on the low resistivity material of greater thickness than the remainder to prevent electrical separation of remote parts of the low resistivity material from the contact (caused by the enhanced etching rate around the contact). A generally plate-shaped body may have the etching contact at one end and be gradually thinned in a direction away from the contact. With a centrally placed contact the body may , be made thinner in all directions away from the contact. In an embodiment (see Fig. 2) a plurality of semi-conductor islands are formed on an insulating substrate - a low resistivity n-type silicon disc 1 is provided with a thin n-type epitaxial layer 11 of relatively high resistivity within which a grid 10 of low resistivity n- or p-type material is formed by diffusion: the disc is fastened by an adhesive layer 21 to an insulating substrate 22 and masked to leave only the original low resistivity material  exposed; the etching contact is applied to this. To shape the body prior to the main etching it is brought to the vertical position with the contact uppermost and slowly lowered into the etching bath (and if desired slowly raised again - the process may be repeated) - this gives an initial shaping to the body which is then fully immersed to etch away the original low resistivity material and that of the diffused grid - thus islands of the relatively high resistivity material are left on the substrate (Fig. 3, not shown). The islands may be unglued from the substrate to provide separate wafers for further processing. The etching may be carried out in a polythene container using a platinum gauze electrode and a platinum pressure contact to the semiconductor. The (stirred) etchant may consist of 1 vol. part of 50 wt. % aqueous HF and 10 vol. parts H 2 O. The initial shaping of the body may instead be effected by using a similar gradual immersion process in a chemical etching bath. In another embodiment (see Fig. 8) as the end result aplurality of islands of semi-conductor material are provided in the surface of and insulated from a polycrystalline semi-conductor support. An epitaxial layer 82 of relatively high resistivity is provided on a low resistivity substrate 86 and the substrate is shaped as in the previous embodiment so that the etching contact 32 may be provided on a thick portion 87. The shaping may be achieved by etching or by grinding - a grinding jig is described for producing a plane face at a very small angle to the free surface of the epitaxial layer. The epitaxial layer is then etched through in grid pattern to leave islands 82 which are given an oxide or nitride coat before the deposition of the polycrystalline support layer 81. After masking, the original material is etched away to leave the desired structure, Fig. 9 (not shown). If fluoride-containing etches are used the etching is automatically limited by the passivation of the high resistivity material which occurs. Oxide used as insulation may be attacked by the etch but may be replaced by a diffusion masking material such as silicon nitride when devices are formed in the islands (such devices are inter-connected to form an integrated circuit).